Food allergy is a serious health problem, and can be life threatening. Public awareness of food allergies is at an all-time high, in part due to the fact that allergic reactions to foods are being reported more frequently. Up to 160 foods have been found to cause allergic reactions (Hefle, 1996, Crit. Rev. Food Sci. Nutr. 36:69-89).
The most common allergen-containing foods are peanuts, soybeans, tree nuts, cow's milk, eggs, crustacea, and fish (Taylor, 1992, Food Technol., 148-152; Sampson, 1992. Food Technol., 141-144; and Burks, 1992, Food Allergy News, 2:(1) 1). The frequency of food allergy is highest in infancy and early childhood, and decreases with increasing age (Collin-Williams and Levy, 1984, Allergy to food other than milk. In Food intolerance, R. K. Chandra, ed., pp. 137-186. Elsevier, N.Y.). About 5% of children younger than three and 1.5% of the general population experience food allergy disorders, or about 4 million Americans suffer from food allergies (Sampson, 1997, JAMA 1997, 278 (22): 1888-1894).
Food allergies are increasing worldwide, and peanut is one of the most allergenic food products. It is estimated that over 600,000 children in the United States have peanut allergies. While childhood allergies to egg and cow's milk may disappear, allergies to nuts, peanuts, soybeans, fish and shellfish tend to persist for the lifetime of the individual (Bock, 1982. J. Allergy Clin. Immunol., 69:173-177; Collin-Williams and Levy, 1984, supra).
Hypersensitive responses to peanut allergens can be fatal. Contact with the slightest amount of peanut protein can be life threatening to particularly sensitive individuals. There is little data on the incidence of near-fatal and fatal allergic reactions to food, but peanut has been documented as a top offender (Taylor, 1987, Nutritional Toxicol. 2: 173-177; Yunginger et al., 1988, JAMA 260:(10) 1450-1452; Evans et al., 1988, CMAJ, 139: (8) 231-232.; Burks et al. 1992; Bock 1992, J. Allergy Clin. Immunol., 90:683-685). It is reported that approximately 125 people die each year in the USA of food-induced anaphylaxis (Burks et al., 1999, Arch Allergy Immunol, 119 (3):165-172.)
The allergy can show up at the first exposure to peanuts, often before the age of three. Most people develop peanut allergies early in life, and few ever grow out of peanut allergies, even in adulthood. Allergic reactions to peanuts are often acute and severe (Sampson, 1990. Peanut anaphylaxis. J. Allergy Clin. Immunol. 86:1-3). The most common manifestation of peanut allergy is acute hives (or urticaria) following exposure. However, some patients may rapidly develop severe angiodema, swelling of the face, bronchospasm and anaphylaxis, following exposure. Some individuals are so sensitive that they will develop symptoms if they kiss someone who has eaten peanuts or if they eat out of a food utensil that has been in contact with peanuts.
Peanut (Arachis hypogaea), a crop grown worldwide, is an annual plant belonging to the family Leguminosae, native to South America, and is commercially grown in the southeastern regions of the United States, specifically in Alabama, Florida, Georgia, North Carolina, and Virginia, and in many other countries of the world. In the United States, several types are grown, although the three most popular peanut types are the Virginia, Spanish, and runner varieties. Virginia peanuts are used primarily for whole kernel consumption and confections. Runner types are used most frequently for oil production and peanut butter (Woodroof, 1983. In: Peanuts: Production, Processing, Products, Woodroof, Ed., Westport, Conn.). Most of the peanut crop in the United States is used for the production of peanut butter. The most widely cultivated peanut cultivars in the USA are ‘Florunner’, ‘New Mexico Valencia’, ‘Georgia Green’, and ‘Georgia Red’.
Although information about the nature and identity of allergenic components of foods is quite limited, it is known that food allergens are most often proteins (Nordlee, et al., 1981., J. Allergy Clin. Immunol., 68:376-383), and provoke an abnormal immunoglobulin E-(IgE) mediated immunological reaction. Several allergenic peanut proteins have been isolated, identified, characterized and classified as minor or major allergens. (Burks A W, Williams L W, Helm R M, Connaughton C, Cockrell G, O'Brien T., J Allergy Clin Immunol 1991; 88:172-179; Burks A W, Cockrell G, Connaughton C, Helm R M.; J Allergy Clin Immunol 1994; 93:743-750; Gleeson P A, Jermyn M A., J Plant Physiol 1977; 4, 25; Kleber-Janke T, Crameri R, Appenzeller U, Becker W M, Schlaak M., Int Arch Allergy Immunol 1999; 119:265-274; Rabjohn P, Helm E M, Stanley J, West C M, Sampson H, Burks A W, Bannon G A., J Clin Invest 1999; 103(4):535-542; Sachs M I, Jones R T, Yunginger J W., J Allergy Clin Immunol 1981; 67(1):27-34; Stanley J S., www.ncbi.nlm.nih.gov/htbin . . . ery?uid=1236995, 1996)
These proteins include glycoproteins, arachin, conarachin, peanut agglutinin and peanut phospholipase. Of these peanut protein allergens, six were classified as major allergens, with an estimated molecular weights of 44, 40, 33, 21, 20, and 18 kDa (De Jong et al., 1998, Clin. Exp. Allergy, 28: 743-751).
Burks et al. 1992 (J. Allergy Clin. Immunol. 90: 962-969) identified two major peanut allergens, designated Ara h 1 and Ara h 2, which are glycoproteins with isoelectric points and molecular weights of 4.55 and 63,500 Daltons and 5.2 and 17,000 Daltons, respectively. These peanut allergens are stable at a temperature of up to 100° C., at pH conditions between pH 2.8 and pH 10, and resistant to digestion by acid and digestive enzymes. Peanut, peanut butter, and peanut flour retain their allergenicity through processing, and crude peanut oil may also be contaminated with these proteins.
The allergens Ara h1 and Ara h2 are found in the cotyledon of peanut, and both are recognized by more than 90% of peanut-sensitive patients, establishing them as major allergens. Ara h1 has been isolated and a cDNA clone produced and sequenced, making this the first peanut allergen to be sequenced (Burks, et al., 1996, J. Clin. Invest. 96, 1715-1721). The partial cDNA sequences of Ara h2 (Stanley et al., 1997, Arch. Biochem. and Biophys, 342:244-253), Ara h3 (Rabjohn, et al., 1999, J. Clin. Invest. 103:535-542), Ara h4, Ara h6, and Ara h7 (Kleber-Janke, et al., 1999, Int. Arch. Allergy Immunol., 119:265-274) have also been recently cloned and sequenced.
Currently, no treatment exists for food allergies. Administration of epinephrine and antihistamines is used to reverse the symptoms of food-allergic reactions. Thus, the most effective management strategy in the prevention of peanut allergies is complete avoidance of peanut-containing foods (Schmidl, et al., 1994, Food Technol. 10:77-85). However, this is difficult to do, as it requires diligent reading of labels and ingredient listings.
The peanut is a popular and important food, and provides a cheap source of protein and oil for human and animal consumption. Peanuts provide niacin, magnesium, Vitamin C, manganese and chromium in significant amounts and smaller amounts of potassium, Vitamin B6, folic acid, phosphorus, copper and biotin. Furthermore, peanut is widely used in both western and oriental cooking, and is added to a variety of foods such as pastries, sandwiches, egg rolls, chili, syrups, flours, sauces, and confections (Nordlee et al., 1981; Yunginger et al., 1988; Evans et al., 1988; Burks et al., 1991). Because dining out is prevalent in the current American lifestyle, the social stigma associated with refraining from taking part in restaurant or party meals by allergic individuals because of the potential threat for accidentally ingesting peanut, makes the strict avoidance of peanut unlikely and unrealistic (Heiner and Navin, 1975, J. Allergy Clin. Immunology 55:82). For example, one of Britain's most promising young athletes died in June 1999, after suffering a seizure triggered by an accidental ingestion of peanut while eating a chicken sandwich (The Independent-London-Jun. 21, 1999).
An investigation of a wide variety of commercially grown peanuts showed no naturally occurring allergen-free peanut lines. (Dodo H W, Marsic D, Mallender M, Cebert E, Viquez O M. Submitted to J. Allergy Clin. Immunology, 2000).
Therefore, there is a need for an alternative solution for the allergic individual. Specifically, there is a need for allergen-free peanut plants, peanuts, and peanut products.
There is also a need for purified peanut allergen proteins which will enable the production of allergen-specific antibodies for detection of allergen in food products, and for prophylaxis and treatment of allergic reactions to peanut.
Modern tools of molecular biology have the potential to offer new transgenic allergen-free peanuts to the peanut-allergic population and the peanut industry. Therefore, an understanding of the molecular structure and regulatory features of the genes is needed to provide needed information for gene silencing and production of allergen-free peanut seeds.